Field programmable gate array incorporating dedicated memory stacks

ABSTRACT

A field programmable gate array, an access lead network coupled to the FPGA, and a plurality of memories electrically coupled to the access lead network. The FPGA, access lead network, and plurality of memories are arranged and configured to operate with a variable word width, namely with a word width between 1 and a maximum number of bits. The absolute maximum word width may be as large as m.times.N where m is the number of word width bits per memory chip and N is the number of memory chips.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 10/347,038, “Field Programmable Gate Array With AVariably Wide Word Width Memory”, filed Jan. 17, 2003, now U.S. Pat. No.6,856,167, which in turn is related to U.S. Provisional PatentApplication Ser. No. 60/384,582, filed on May 31, 2002, which isincorporated herein by reference and to which priority is claimedpursuant to 35 USC 119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electronic module and in particular to acombination of a memory array with a field programmable gate array.

2. Description of the Prior Art

Of the many varieties of integrated circuits available on the markettoday, field programmable gate arrays (FPGAs) are particularly usefulwhen building many kinds of electronic devices and systems. BecauseFPGAs allow the designer to integrate complex logic that is peculiar tohis application in one or perhaps a few integrated circuits withoutsuffering the cost, delay and risk that typically are incurred whendesigning a custom integrated circuit, use of FPGAs greatly reduce bothdesign cost and time-to-market for new products.

Not withstanding the great utility of FPGAs, there exist severallimitations to the usefulness of these devices. As suggested by FIG. 1,one of the limitations is that FPGAs are typically designed based on adesign rule that assumes a fixed and limited word width which isparticularly limiting when used in combination with a large amount ofmemory in high performance applications such as data processing andnetworking. Further, when the FPGA is used to read from and write into amemory array that is arranged in a typical planar fashion, aconsiderable amount of space on the printed circuit board is required inorder to physically provide for the combination of the FPGA and thememory. Even when space is available for a large planar area thatsupports the FPGA and surrounding memory, large areas inherentlyincrease parasitics and degrade performance.

What is needed is some type of packaging concept for an FPGA andassociated memory array which overcomes these limitations in the priorart.

BRIEF SUMMARY OF THE INVENTION

The invention is embodied by a field programmable gate array, an accesslead network coupled to the FPGA, and a plurality of memorieselectrically coupled to the access lead network. The FPGA, access leadnetwork, and plurality of memories are arranged and configured tooperate with a variable word width, namely with a word width between 1and a maximum number of bits. The absolute maximum word width may be aslarge as m.times.N where m is the number of word width bits per memorychip and N is the number of memory chips.

A first preferred embodiment of the invention is an apparatus comprisinga field programmable gate array (FPGA), an access lead network formedfrom an interposer board electrically coupled and proximate to the FPGA,and a plurality of memories electrically coupled and proximate to theinterposer board on an opposite side thereof to the FPGA.

The FPGA is coupled to the interposer board through a first ball gridarray. The plurality of memories are coupled to the interposer boardthrough a second ball grid array. The plurality of memories arepreferably stacked to collectively form a memory block having an upperand lower contact surface and where the second ball grid array isdisposed on both the upper and lower contact surfaces. Whether the ballgrid arrays are disposed on the memory block, the interposer board orthe FPGA is a matter of choice and convenience. Hence, although it maylater be stated, for example, that the first ball array is disposed onthe interposer board, it is equivalent to state that the first ballarray is disposed on the FPGA or both. For the purposes of thisspecification any statement that a ball grid array is disposed on one oftwo adjacent structures should be understood as meaning that the ballgrid array is disposed on the other one of the two adjacent structuresor both.

The apparatus further comprises a plurality of interleaved lines. Theportion of the second ball grid array on the upper contact surface isdirectly coupled to the interposer board and where the portion of thesecond ball grid array on the lower contact surface is coupled to theinterposer board through the plurality of interleaved lines.

The apparatus further comprises an insulatively filled layer disposedbetween adjacent ones of the plurality of memories in which layer theinterleaved lines are disposed.

The apparatus further comprises at least one resistor and capacitorcombination coupled to a corresponding one of the plurality of memories,the resistor and capacitor combination being disposed in theinsulatively filled layer.

It is to be expressly understood that the invention also includes themethod of fabricating the apparatus disclosed above.

A second preferred embodiment of the invention is an apparatuscomprising a field programmable gate array (FPGA), an access leadnetwork formed from an interposer board electrically coupled andproximate to the FPGA, and a plurality of memories electrically coupledand proximate to the interposer board on the same side thereof as theFPGA.

While the apparatus and method has or will be described for the sake ofgrammatical fluidity with functional explanations, it is to be expresslyunderstood that the claims, unless expressly formulated under 35 USC112, are not to be construed as necessarily limited in any way by theconstruction of “means” or “steps” limitations, but are to be accordedthe full scope of the meaning and equivalents of the definition providedby the claims under the judicial doctrine of equivalents, and in thecase where the claims are expressly formulated under 35 USC 112 are tobe accorded full statutory equivalents under 35 USC 112. The inventioncan be better visualized by turning now to the following drawingswherein like elements are referenced by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic view of a conventional bused interfacebetween an FPGA and a planar-arranged memory array where the word widthis fixed and limited to a physical bus width of only m-bits.

FIG. 2 is an simplified schematic view of a memory enhanced gate arrayaccording to a generalized embodiment of this invention where all memorybits are simultaneously available to the FPGA such that the FPGA,incorporating suitable logic, can implement a virtual word with of anydesired width from 1 to m.times.N bits.

FIG. 3 is a diagrammatic end view of a memory enhanced gate arrayaccording to a first preferred embodiment of the invention.

FIG. 4 is a diagrammatic side view of the memory enhanced gate array ofFIG. 3.

FIG. 5 is a diagrammatic end view of a memory enhanced gate arrayaccording to a second preferred embodiment of the invention.

FIG. 6 is an exploded perspective view of a memory stack used in thememory enhanced gate array of FIG. 5.

FIG. 7 is a perspective view and close-up enlargement of a memoryenhanced gate array of FIG. 5.

The invention and its various embodiments can now be better understoodby turning to the following detailed description of the preferredembodiments which are presented as illustrated examples of the inventiondefined in the claims. It is expressly understood that the invention asdefined by the claims may be broader than the illustrated embodimentsdescribed below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is an simplified schematic view of a memory enhanced gate arrayaccording to a generalized embodiment of this invention a fieldprogrammable gate array (FPGA) has simultaneous access to all memorybits such that the FPGA, incorporating suitable logic, can implement avirtual word with of any desired width from 1 to m.times.N bits. Variousparticular embodiments are possible, two of which will now be discussed.

FIGS. 3 and 4 relate to a first preferred embodiment where an FPGA iscoupled to an access lead network formed, in this particular case, by aproximate interposer board and a first ball grid array. A plurality ofmemories are coupled to the proximate interposer board through a secondball grid array. As discussed above, the FPGA operates with a variableword width. The plurality of memories are stacked to form a memoryblock. Each individual access lead to the memory in each layer of thememory stack is brought to the edge of the stack. Therefore, the FPGAcan connect to a large memory array at any desired word width from 1 tom.times.N, i.e. from 1 to the maximum number of bits in the memoryarray. The second ball grid array is disposed on both the upper andlower contact surfaces of the memory block. The portion of the secondball grid array on the upper contact surface is directly coupled to theinterposer board. The portion of the second ball grid array on the lowercontact surface is coupled to the interposer board through a pluralityof interleaved lines. An insulatively filled layer is disposed betweenadjacent ones of the plurality of memories in which layer theinterleaved lines are disposed.

The first preferred memory enhanced gate array 10 is illustrated in adiagrammatic assembled end view in FIG. 3 and in a diagrammaticassembled side view in FIG. 4. The memory enhanced gate array 10 isfabricated using a stacked architecture such as that developed by IrvineSensors and generally described in Irvine Sensors issued patents.Stacked architectures are characterized by high port density and lowpower consumption. As shown in FIGS. 3 and 4 a field programmable gatearray (FPGA) 12 is disposed on a first side of an interposer board 14through a conventional ball grid array 18 connection therebetween. AnyFPGA now available or later devised may be used.

In this particular embodiment, the Interposer board 14 that forms theaccess lead network is an insulating printed circuit board having afirst surface (the topside in the picture) with a contact patternarranged and configured to connect to the ball grid array 18 of FPGA 12and having a plurality of vias 17 defined therethrough connecting ballgrid array 18 with a contact pattern arranged and configured to connectto the ball grid array 20 on a second surface (the underside in thepicture).

Disposed adjacent the second side of the interposer 14 in an edgewisefashion are a plurality of memory integrated circuits 16. Memoryintegrated circuits 16 are organized in a “loaf fashion”, that is eachcircuit 16 is thought of as a “slice of bread” stacked together tocollectively form a “loaf” with a first side of the loaf in contact withinterposer board 14. Greater detail concerning the “loaf” architectureis disclosed in U.S. patent application Ser. No. 09/339,023, filed onJan. 9, 2003, and entitled “METHOD FOR MAKING STACKED INTEGRATEDCIRCUITS (ICs) USING PREPACKAGED PARTS”, which is incorporated herein byreference. In the illustrated embodiment, the memory integrated circuits16 are synchronous dynamic random access memories (SDRAMs).

The leads of memory integrated circuits 16 are connected directly toball grid array 20 in the case of the leads exiting memory integratedcircuits 16 on first ends of memory integrated circuits 16 nearinterposer board 14 and through interleaved lines 24 between memoryintegrated circuits 16 in the case of leads on the lower ends of memoryintegrated circuits 16 disposed away from interposer board 14. Theinterleaved lines 24 are connected to ball grid array 22 on a secondsurface (the bottom as shown) of memory enhanced gate array 10 which inturn are coupled to the leads of memory integrated circuits 16 disposedaway from interposer board 14. Interleaved lines 24 are then led upwardthrough an insulatively filled layer 26 and connected into ball gridarray 20 next to the upper ends of integrated circuits 16 adjacent tointerposer board 14. Also included in layer 26 is a conventionaldiscrete or integrated circuit resistor and capacitor combination 28coupled in a conventional manner with integrated circuits 16 to optimizememory speed.

An FPGA 12 used in connection with this invention may be arranged andconfigured as disclosed in U.S. patent application Ser. No. 09/346,363,filed on Jan. 17, 2003, entitled “METHOD FOR EFFECTIVELY EMBEDDINGVARIOUS INTEGRATED CIRCUITS WITHIN FIELD FROGRAMMABLE GATE ARRAYS”,which is incorporated herein by reference. As there disclosed, FPGA 12operates with a parameterized word width which can be configured orfield programmed as suggested by block 13 labeled “variable word withlogic.” Hence, in the illustrated embodiment, the memory block of memoryenhanced gate array 10 operates so that the memory is addressable inword widths of 1 to m.times.N bits.

It is a further advantage of the invention that FPGA 12 and moreimportantly, its leads are in very close proximity to the addressableleads of memories 16, thereby avoiding a host of timing and capacitanceproblems that can arise when the FPGA and the memory array are separatedby substantially longer line lengths as occurs on a conventional flat orplanar printed circuit board layout.

There is no bus-width related processor-to-memory bottleneck with thearchitecture of the invention and there is negligible response skew ascompared with a hypothetical, simultaneous connection to multiple memorychips arranged on a planar substrate. In a conventional bussed andplanar arrangement of memory, the maximum transfer rate is m bitsmultiplied by the clock speed. In a memory enhanced gate array accordingto this invention, however, the maximum transfer rate is m.times.N bitstimes the clock rate. Skew is minimized because the equal lead lengthtopology associated with the embodiments of this invention makes itunnecessary to account for different response times to differentlylocated memory circuits.

Further the invention is characterized by “virtual” memory modularityand a hidden memory-to-pin configuration. The virtual memory modularityarises from the fact that the invention permits m.times.N bits of memoryto be accessed in any desired word with from 1 bit to m.times.N bits. Byway of example, sixteen 1 GB memory chips that are 18 bits wide could beaddressed as any one of the following configurations, and more:

1 GB memory with 18.times.16 word width

2 GB memory with 18.times.8 word width

4 GB memory with 18.times.4 word width

16 GB memory with 18.times.1 word width

FIGS. 5 to 7 illustrate a memory enhanced gate array 110 according to asecond preferred embodiment of the invention. The embodiment is still anapparatus comprising a field programmable gate array (FPGA) 112, anaccess lead network formed from an interposer board 114 electricallycoupled and proximate to the FPGA, and a plurality of memory electronicintegrated circuits 116 that electrically coupled and proximate to theinterposer board. There are, however, certain implementationdifferences.

For example, the memory ICs 116 are ball grid array (BGA) packages andthey are connected (through a printed circuit board 121 and a connector128) to the same side of the interposer board 114 as the FPGA 112. Asbetter shown in FIG. 6, the second embodiment 110 features PCBAssemblies 121 where the memory ICs 116 are mounted to opposite sides ofthe printed circuit board 126 with resistors and capacitors 128 asrequired. As suggested by FIG. 6, the PCB assemblies 121 are suitablyarranged to form an overall memory stack 130. Two such stacks 130, 130are disposed on either side of the FPGA 112 as shown in FIG. 5, butfewer or more stacks may be used.

As shown in FIG. 7, the memory stacks 130 are complete by introducing anencapsulation material 126 between the layers of the stack, and thenusing suitable metallization techniques to form I/O pads 127 on theresulting planar edge of the stack 130. The I/O pads 127 of the finishedstack are ultimately mated to a connector 128 using conventional BGAconnectors 129 as shown in FIG. 5.

Another difference between the first and second embodiments is that inthe second embodiment, as shown in FIG. 5, the memory stacks 130 areconnected to the interposer board 114 with a pin grid array 118 ratherthan directly to the interposer with a ball grid array. The overallmemory enhanced gate array 110 is also connected to a user board with apin grid array 122 rather than with a ball grid array. The foregoingelectromechanical interconnection between the FPGA, the memories and theuser board are just two examples and any desired method ofinterconnection may be used.

It is possible, of course, to couple the plurality of memories to theFPGA at a die level, using suitable metallization techniques, ratherthan using a discrete interposer board as in the first two embodiments.

Many other alterations and modifications may be made by those havingordinary skill in the art without departing from the spirit and scope ofthe invention. Therefore, it must be understood that the illustratedembodiment has been set forth only for the purposes of example and thatit should not be taken as limiting the invention as defined by thefollowing claims. For example, notwithstanding the fact that theelements of a claim are set forth below in a certain combination, itmust be expressly understood that the invention includes othercombinations of fewer, more or different elements, which are disclosedin above even when not initially claimed in such combinations.

The words used in this specification to describe the invention and itsvarious embodiments are to be understood not only in the sense of theircommonly defined meanings, but to include by special definition in thisspecification structure, material or acts beyond the scope of thecommonly defined meanings. Thus if an element can be understood in thecontext of this specification as including more than one meaning, thenits use in a claim must be understood as being generic to all possiblemeanings supported by the specification and by the word itself.

The definitions of the words or elements of the following claims are,therefore, defined in this specification to include not only thecombination of elements which are literally set forth, but allequivalent structure, material or acts for performing substantially thesame function in substantially the same way to obtain substantially thesame result. In this sense it is therefore contemplated that anequivalent substitution of two or more elements may be made for any oneof the elements in the claims below or that a single element may besubstituted for two or more elements in a claim. Although elements maybe described above as acting in certain combinations and even initiallyclaimed as such, it is to be expressly understood that one or moreelements from a claimed combination can in some cases be excised fromthe combination and that the claimed combination may be directed to asubcombination or variation of a subcombination.

Insubstantial changes from the claimed subject matter as viewed by aperson with ordinary skill in the art, now known or later devised, areexpressly contemplated as being equivalently within the scope of theclaims. Therefore, obvious substitutions now or later known to one withordinary skill in the art are defined to be within the scope of thedefined elements.

The claims are thus to be understood to include what is specificallyillustrated and described above, what is conceptually equivalent, whatcan be obviously substituted and also what essentially incorporates theessential idea of the invention.

1. An apparatus comprising: a field programmable gate array (FPGA); anaccess lead network electrically coupled and proximate to the FPGA; atleast one memory stack external of said FPGA and electrically coupled toan interposer board, said memory stack defining at least one planar edgeand comprised of a plurality of layers wherein each of said layerscomprises at least one memory IC; and, said memory stack furthercomprising at least one conductive I/O pad on said at least one planaredge for the routing of an electrical signal between said at least onememory IC and said interposer board.
 2. The apparatus of claim 1 wherethe FPGA is arranged and configured to operate with a variable wordwidth.
 3. The apparatus of claim 1 where the access lead network is aninterposer board.
 4. The apparatus of claim 2 where the FPGA is arrangedand configured to operate with a word width between 1 to m.times.N bitswhere m is the number of bits in the word width of each of said memoryICs and N is the number of said memory ICs in said stack.